SuziQ,
Without knowing which tank (brand and part number) you ordered, first guess on the "bolt" at the bottom instead of a metal fitting make me think the bolt is just there to act as a plug to keep debris out of the tank before installation. There is a fitting there, just not same as original design and installed differently than the way your old tank was constructed.
From your new tank/old tank pictures, it's clear that the new tank fitting was applied on the inside of the tank and spot welded (4 visible weld dots) and sealed on the inner part of the tank instead of the way the original tank was made with the bulk of the fitting on the outer face of the tank.
Removing that bolt should leave you with a threaded hole to accept the bottom of the tank fuel line fitting/shut-off valve assembly from your original tank (assuming of course they used the proper fitting on the new tank).
A word of caution on this threaded fitting hole. Double check the thread and hole size against your existing fitting/valve if transferring from the original tank. I have seen it posted in here sometime in the past that some reproduction tanks (don't remember brand) use a metric threaded opening instead of the us standard size. Will cause you some grief trying to get your fuel line connection/shut-off valve installed into the new tank if they aren't a match.
We may be able to offer more info if you can post the brand and part number of the new tank.
Dan
EDIT: Otto beat me to the punch with a shorter but accurate answer. Still wouldn't hurt to confirm your hole and thread size before trying to install the fitting.
